Modern semiconductor lasers (SL) cover broad spectrum range from UV to mid-IR. The compact size, efficient light generation, low cost of manufacturing and maintaining have become a key to successful commercial applications of SL. The main shortcoming of SL is its low emitted power value (below 1 W, as compared with solid state lasers (SSL), which can reach several kW). However SSL emission wavelengths are restricted only to discrete values of electronic transitions in ions.
Vertical-external-cavity surface-emitting lasers (VECSEL) combine the advantages of SSL and SL in one device. Optically pumped VECSELs offer fundamental transverse mode operation, circular optical beam and scaling of the emitted power from one tenth up to tens of watts. Such efficient power scaling in a range of four orders of magnitude and maintaining good beam quality with a low divergence is enabled by the laser mode and pump spot-size scalability on the VECSEL semiconductor laser chip. VECSELs give access to wide output wavelength range by gain media engineering and capability to determine the specific desired wavelength by means of intra-cavity tunable filters, control of transverse modes realized by the optical cavity. Open laser cavity allows for laser beam interaction with optical elements, such as nonlinear optical crystals for higher harmonics generation, saturable absorbers for short pulse passive mode locking, etc.
Since VECSELs are designed for high-power operation, the thermal management issue is of major importance. Typically 30% power of pump light is transformed into the output light, 20% is reflected back from the chip and 50% percent is wasted as heat. The improvement of heat transport from the active mirror to the heat-sink can increase the efficiency of the device and will assure more stable laser action.